1. Field of the Invention
This invention relates to a communication scheduling method suitable for P-MP (i.e., Point-to-Multipoint) wireless data communication via relay stations.
2. Description of the Related Art
A process for assigning transmission opportunities is called “scheduling.” In a FIFO (First In First Out) which is the simplest algorithm, only one queue is prepared for all flows, and input packets are queued in order of arrival, and are scheduled in this order. In other words, a packet that has arrived earlier than the others is output earlier. However, in the FIFO, real-time traffic, such as that in telephone communication or video communication, which is strict about time, and non-real-time traffic, such as that in file transfer, web browsing, or E-mail transmission, are queued in a mixed state, thus making it difficult to guarantee QoS (i.e., Quality of Service).
A non-patent document 1 (IEEE Standard for Local and metropolitan area networks-Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE 802.16-2004, October, 2004) discloses a high-speed wireless access system that is called “IEEE802.16” (hereinafter, referred to simply as “802.16”), by which a QoS control function is supported. Latency, jitter, traffic rate, etc., of packets can be mentioned as QoS parameters in the “802.16.” These parameters are guaranteed between base stations or between a base station and a subscriber station, not between end users. In other words, for example, in a downlink, Latency or jitter to be guaranteed is the one that occurs until a packet is sent to a subscriber station after a base station receives this packet. The “802.16” does not have an especially specified scheduling algorithm.
The “802.16” can fulfill a QoS guarantee, but does not disclose a detailed scheduling algorithm for the guarantee. Therefore, the “802.16” is required to have a scheduling algorithm that enables such a QoS guarantee. Additionally, to achieve a multihop network in which the “802.16” is wirelessly relayed, a scheduling method taking relays into consideration must be established.